Reactor with advanced architecture for the electrochemical reaction of co2, co and other chemical compounds

ABSTRACT

A platform technology that uses a novel membrane electrode assembly, including a cathode layer, an anode layer, a membrane layer arranged between the cathode layer and the anode layer, the membrane conductively connecting the cathode layer and the anode layer, in a COx reduction reactor has been developed. The reactor can be used to synthesize a broad range of carbon-based compounds from carbon dioxide and other gases containing carbon.

STATEMENT OF GOVERNMENT SUPPORT

The Government has rights in this invention pursuant to a User AgreementFP00003032 between Opus 12, Incorporated and The Regents of theUniversity of California, which manages and operates Ernest OrlandoLawrence Berkeley National Laboratory for the US Department of Energyunder Contract No. DE-ACO2-05CH11231.

INCORPORATION BY REFERENCE

An Application Data Sheet is filed concurrently with this specificationas part of the present application. Each application that the presentapplication claims benefit of or priority to as identified in theconcurrently filed Application Data Sheet is incorporated by referenceherein in its entirety and for all purposes.

TECHNICAL FIELD

The present disclosure generally relates to the field of electrochemicalreactions, and more particularly, to devices and methods forelectrochemically reducing CO_(x) (CO₂, CO, or combinations thereof)into carbon-containing chemical compounds.

BACKGROUND

Anthropogenic CO₂ emissions have been linked to climate change.

As a response to increasing concerns about global greenhouse gasemissions, technologies that can recycle CO₂ into high-value productshave received growing interest.

Electrochemical reduction of CO_(x) (CO₂, CO, or combinations thereof)combines just three inputs: CO_(x), a source of protons, andelectricity, and converts them into fuels, chemicals, and other productssuch as methanol, ethanol, carbon monoxide and acetic acid. However, ithas not been possible to achieve industrial-scale production of suchfuels and chemicals. One barrier has been the lack of a suitableelectrochemical reactor. One difficulty in achieving an efficientreactor using conventional designs is the poor transport of CO_(x) tothe catalyst surface in the reactor due to the low solubility of CO_(x)in aqueous solutions and the inability to control the competing waterreduction reaction that leads to hydrogen production.

This disclosure describes a new and useful electrochemical reactor forreduction of CO_(x) that addresses the aforementioned disadvantages ofconventional reactors. Gas-phase CO_(x), as opposed to CO_(x) dissolvedin water, can be supplied to the reactor to achieve efficient transportand product production rates. The ion conducting polymer surrounding theCO_(x) conversion catalyst minimizes the competing hydrogen formationreaction. The reactor has high energy efficiency, high current density,fast response time, and robustness, while also providing flexibility inthe kinds of chemical products it can produce.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing aspects and others will be readily appreciated by theskilled artisan from the following description of illustrativeembodiments when read in conjunction with the accompanying drawings.

FIG. 1 shows a standard membrane electrode assembly used in aconventional water electrolysis reactor, which makes hydrogen andoxygen.

FIG. 2 is a schematic illustration of a membrane electrode assembly foruse in a new CO_(x) reduction reactor (CRR), according to an embodimentof the invention.

FIG. 3 is a schematic drawing that shows a possible morphology for twodifferent kinds of catalysts supported on a catalyst support particle,according to an embodiment of the invention.

FIG. 4 is a schematic illustration of a membrane electrode assembly foruse in a new CRR, according to another embodiment of the invention.

FIG. 5 is a schematic drawing that shows the membrane electrode assemblyfor use in a new CRR, according to yet another embodiment of theinvention.

FIG. 6 is a schematic drawing that shows the major components of aCO_(x) reduction reactor (CRR), according to an embodiment of theinvention.

FIG. 7 is a schematic drawing that shows the major components of a CRRwith arrows showing the flow of molecules, ions, and electrons accordingto one embodiment of the invention.

FIG. 8 is a schematic drawing that shows the major inputs and outputs ofthe CRR reactor.

SUMMARY

In one embodiment of the invention, a membrane electrode assembly (MEA)for use in a CO_(x) reduction reactor is provided. The MEA has a cathodelayer comprising reduction catalyst and a first ion-conducting polymerand an anode layer comprising oxidation catalyst and a secondion-conducting polymer. There is a polymer electrolyte membranecomprising a third ion-conducting polymer between the anode layer andthe cathode layer. The polymer electrolyte membrane provides ioniccommunication between the anode layer and the cathode layer. There isalso a cathode buffer layer comprising a fourth ion-conducting polymerbetween the cathode layer and the polymer electrolyte membrane, thecathode buffer. There are three classes of ion-conducting polymers:anion-conductors, cation-conductors, and cation-and-anion-conductors. Atleast two of the first, second, third, and fourth ion-conductingpolymers are from different classes of ion-conducting polymers.

In one arrangement, the reduction catalyst is selected from the groupconsisting of V, Cr, Mn, Fe, Co, Ni, Cu, Sn, Zr, Nb, Mo, Au, Ru, Rh, Pd,Ag, Cd, Hf, Ta, W, Re, Ir, Pt, Hg, Al, Si, In, Ga, Tl, Pb, Bi, Sb, Te,Sm, Tb, Ce, and Nd, and combinations thereof, and/or any other suitablereduction catalysts. The reduction catalyst can further compriseconductive support particles selected from the group consisting ofcarbon, boron-doped diamond, fluorine-doped tin oxide, and combinationsthereof, and/or any other suitable reduction catalysts.

In one arrangement, the cathode layer comprises between 10 and 90 wt %first ion-conducting polymer. The first ion-conducting polymer cancomprise at least one ion-conducting polymer that is an anion-conductor.

The first ion-conducting polymer can comprise one or morecovalently-bound, positively-charged functional groups configured totransport mobile negatively-charged ions. The first ion-conductingpolymer can be selected from the group consisting of aminatedtetramethyl polyphenylene; poly(ethylene-co-tetrafluoroethylene)-basedquaternary ammonium polymer; quaternized polysulfone), blends thereof,and/or any other suitable ion-conducting polymers. The firstion-conducting polymer can be configured to solubilize salts ofbicarbonate or hydroxide.

The first ion-conducting polymer can comprise at least oneion-conducting polymer that is a cation-and-anion-conductor. The firstion-conducting polymer can be selected from the group consisting ofpolyethers that can transport cations and anions and polyesters that cantransport cations and anions. The first ion-conducting polymer can beselected from the group consisting of polyethylene oxide, polyethyleneglycol, polyvinylidene fluoride, and polyurethane.

In one arrangement, the oxidation catalyst is selected from the groupconsisting of metals and oxides of Ir, Pt, Ni, Ru, Pd, Au, and alloysthereof, IrRu, PtIr, Ni, NiFe, stainless steel, and combinationsthereof, and/or any other suitable metals or metal oxides. The oxidationcatalyst can further contain conductive support particles selected fromthe group consisting of carbon, boron-doped diamond, and titanium.

In one arrangement, the anode layer comprises between 5 and 95 wt %second ion-conducting polymer. The second ion-conducting polymer cancomprise at least one ion-conducting polymer that is a cation-conductor.

The second ion-conducting polymer can comprise one or more polymers thatcontain covalently-bound, negatively-charged functional groupsconfigured to transport mobile positively-charged ions. The secondion-conducting polymer can be selected from the group consisting ofethanesulfonyl fluoride,2[1-[difluoro-[(trifluoroethenyl)oxy]methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2,-tetrafluoro-,with tetrafluoroethylene,tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acidcopolymer, other perfluorosulfonic acid polymers, blends thereof, and/orany other suitable ion-conducting polymer.

In one arrangement, the third ion-conducting polymer comprises at leastone ion-conducting polymer that is a cation-conductor. The thirdion-conducting polymer can comprise one or more covalently-bound,negatively-charged functional groups configured to transport mobilepositively-charged ions. The third ion-conducting polymer can beselected from the group consisting of ethanesulfonyl fluoride,2-[1-[difluoro-[(trifluoroethenyl)oxy]methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2,-tetrafluoro-,with tetrafluoroethylene,tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acidcopolymer, other perfluorosulfonic acid polymers, blends thereof, and/orany other suitable ion-conducting polymer.

In one arrangement, the cathode buffer layer has a porosity between0.01% and 95% (e.g., approximately between, by weight, by volume, bymass, etc.). However, in other arrangements, the cathode buffer layercan have any suitable porosity (e.g., between 0.01-95%, 0.1-95%,0.01-75%, 1-95%, 1-90%, etc.).

In one arrangement, the fourth ion-conducting polymer comprises at leastone ion-conducting polymer that is an anion-conductor. The fourthion-conducting polymer can comprise one or more covalently-bound,positively-charged functional groups configured to transport mobilenegatively-charged ions. The fourth ion-conducting polymer can beselected from the group consisting of aminated tetramethylpolyphenylene; poly(ethylene-co-tetrafluoroethylene)-based quaternaryammonium polymer; quaternized polysulfone; blends thereof; and/or anyother suitable ion-conducting polymer.

In one arrangement, the first ion-conducting polymer and the fourthion-conducting polymer are from the same class. In one arrangement, thesecond ion-conducting polymer and the third ion-conducting polymer arefrom the same class.

In one arrangement, the membrane electrode assembly further comprises ananode buffer layer between the anode layer and the polymer electrolytemembrane, the anode buffer layer comprising a fifth ion-conductingpolymer.

The membrane electrode assembly wherein the fifth ion-conducting polymercomprises at least one ion-conducting polymer that is acation-conductor. The fifth ion-conducting polymer can comprise one ormore covalently-bound, negatively-charged functional groups configuredto transport mobile positively-charged ions.

The fifth ion-conducting polymer can be selected from the groupconsisting of ethanesulfonyl fluoride,2-[1-[difluoro-[(trifluoroethenyl)oxy]methyl]-1,2,2,2-tetrafluoroethoxy]-1,1,2,2,-tetrafluoro-,with tetrafluoroethylene,tetrafluoroethylene-perfluoro-3,6-dioxa-4-methyl-7-octenesulfonic acidcopolymer, other perfluorosulfonic acid polymers, blends thereof, and/orany other suitable ion-conducting polymer. The second ion-conductingpolymer and the fifth ion-conducting polymer can be from the same class.

In one arrangement, the anode buffer layer has a porosity between 0.01%and 95% (e.g., approximately between, by weight, by volume, by mass,etc.). However, in other arrangements, the anode buffer layer can haveany suitable porosity (e.g., between 0.01-95%, 0.1-95%, 0.01-75%, 1-95%,1-90%, etc.).

In another embodiment of the invention, a membrane electrode assembly(MEA) for use in a CO_(x) reduction reactor is provided. The MEA has acathode layer comprising reduction catalyst and a first ion-conductingpolymer and an anode layer comprising oxidation catalyst and a secondion-conducting polymer. There is a polymer electrolyte membrane betweenthe anode layer and the cathode layer. The polymer electrolyte membranecomprises a third ion-conducting polymer and provides ioniccommunication between the anode layer and the cathode layer. There arethree classes of ion-conducting polymers: anion-conductors,cation-conductors, and cation-and-anion-conductors. At least two of thefirst, second, and third ion-conducting polymers are from differentclasses of ion-conducting polymers.

In another embodiment of the invention, CO_(x) reduction reactor isprovided. The reactor has at least one electrochemical cell, whichcomprises any of the membrane electrode assemblies described herein. Thereactor also has a cathode support structure adjacent to the cathode,the cathode support structure comprising a cathode polar plate, at leastone cathode gas diffusion layer, at least one inlet and at least oneoutlet. There is also an anode cell support structure adjacent to theanode. The anode support structure comprises an anode polar plate and atleast one anode gas diffusion layer, at least one inlet and at least oneoutlet.

In yet another embodiment of the invention, a method of operating aCO_(x) reduction reactor is provided. The method results in productionof reaction products. The process can include: providing anelectrochemical reactor comprising at least one electrochemical cellcomprising a membrane electrode assembly, a cathode support structureadjacent to the cathode that includes a cathode polar plate, at leastone cathode gas diffusion layer, at least one gas inlet and at least onegas outlet, and an anode cell support structure adjacent to the anodethat includes an anode polar plate and at least one anode gas diffusionlayer, at least one inlet and at least one outlet; applying a DC voltageto the cathode polar plate and the anode polar plate; supplying one ormore oxidation reactants to the anode and allowing oxidation reactionsto occur; supplying one or more reduction reactants to the cathode andallowing reduction reactions to occur; collecting oxidation reactionproducts from the anode; and collecting reduction reaction products fromthe cathode.

The oxidation reactants can be selected from the group consisting ofhydrogen, methane, ammonia, water, or combinations thereof, and/or anyother suitable oxidation reactants. In one arrangement, the oxidationreactant is water.

The reduction reactants can be selected from the group consisting ofcarbon dioxide, carbon monoxide, and combinations thereof, and/or anyother suitable reduction reactants. In one arrangement, the reductionreactant is carbon dioxide.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiments are illustrated in the context of reduction ofCO_(x) (CO₂, CO_(x) or combinations thereof) to produce useful chemicalsand fuels. The skilled artisan will readily appreciate, however, thatthe materials and methods disclosed herein will have application in anumber of other contexts where reduction reactions are desirable,particularly where production of a variety of chemicals in a variety ofreaction conditions is important. The reactor used to reduce CO_(x)could also be used to reduce other compounds, including but not limitedto: N₂, SO_(x), NO_(x), acetic acid, ethylene, O₂ and any other suitablereducible compound or combinations thereof.

All publications referred to herein are incorporated by reference intheir entirety for all purposes as if fully set forth herein.

Table 1 lists some abbreviations that are used throughout thisapplication.

TABLE 1 Abbreviation Description CO_(x) CO₂, CO or a combination thereofCRR CO_(x) reduction reactor MEA membrane electrode assembly PEM polymerelectrolyte membrane

The term, “ion-conducting polymer” is used herein to describe a polymerelectrolyte having greater than approximately 1 mS/cm specificconductivity for anions and/or cations. The term, “anion-conductor,”describes an ion-conducting polymer that conducts anions primarily(although there will still be some small amount of cation conduction)and has a transference number for anions greater than approximately 0.85at around 100 micron thickness. The terms “cation-conductor” and/or“cation-conducting polymer” describe an ion-conducting polymer thatconducts cations primarily (e.g., there can still be an incidentalamount of anion conduction) and has a transference number for cationsgreater than approximately 0.85 at around 100 micron thickness. For anion-conducting polymer that is described as conducting both anions andcations (a “cation-and-anion-conductor”), neither the anions nor thecations has a transference number greater than approximately 0.85 orless than approximately 0.15 at around 100 micron thickness. To say amaterial conducts ions (anions and/or cations) is to say that thematerial is an ion-conducting material.

Hydration is useful in effecting ion conduction for most ion-conductingpolymers. Humidification of CO_(x) or anode feed material can be usedfor the delivery of liquid water to the MEA to maintain hydration ofion-conducting polymers.

In one embodiment of the invention, a CO_(x) reduction reactor (CRR)that uses a novel membrane electrode assembly in an electrochemical cellhas been developed. Table 2 lists some examples of useful chemicals thatcan be produced from CO_(x) in such a reactor.

TABLE 2 Exemplary CO₂ and CO Reduction Products Formic Acid CarbonMonoxide Methanol Glyoxal Methane Acetic Acid Glycolaldehyde EthyleneGlycol Acetaldehyde Ethanol Ethylene Hydroxyacetone Acetone AllylAlcohol Propionaldehyde n-Propanol Syngas

Membrane Electrode Assembly

A conventional membrane electrode assembly (MEA) 100 used for waterelectrolysis to make hydrogen and oxygen is shown in FIG. 1. The MEA 100has a cathode 120 and an anode 140 separated by an ion-conductingpolymer layer 160 that provides a path for ions to travel between thecathode 120 and the anode 140. The cathode 120 and the anode 140 eachcontain ion-conducting polymer, catalyst particles, and electronicallyconductive catalyst support. The ion-conducting polymer in the cathode120, anode 140, and ion-conducting polymer layer 160 are either allcation-conductors or all anion-conductors.

The conventional MEA 100 is not suitable for use in a CRR. When all ofthe ion-conducting polymers are cation-conductors, the environmentfavors water reduction to make hydrogen in an unwanted side reaction.The production of hydrogen lowers the rate of CO_(x) product productionand lowers the overall efficiency of the process. When all of theion-conducting polymers are anion-conductors, then CO₂ reacts withhydroxide anions in the ion-conducting polymer to form bicarbonateanions. The electric field in the reactor moves the bicarbonate anionsfrom the cathode side of the cell to the anode side of the cell. At theanode, bicarbonate anions can decompose back into CO₂ and hydroxide.This results in the net movement of CO₂ from the cathode to the anode ofthe cell, where it does not react and is diluted by the anode reactantsand products. This loss of CO₂ to the anode side of the cell reduces theefficiency of the process.

A new membrane electrode assembly (MEA) 200 for use in a CRR is shown inFIG. 2, according to an embodiment of the invention. The MEA 200 has acathode 220 and an anode 240 separated by an ion-conducting polymerlayer 260 that provides a path for ions to travel between the cathode220 and the anode 240. In general, it is especially useful if thecathode and anode layers of the MEA are porous in order to facilitategas and fluid transport and to maximize the amount of catalyst surfacearea that is available for reaction.

The cathode 220 contains a blend of reduction catalyst particles,electronically-conductive support particles that provide support for thereduction catalyst particles, and a cathode ion-conducting polymer.There are tradeoffs in choosing the amount of cathode ion-conductingpolymer in the cathode. It is important to include enough cathodeion-conducting polymer to provide sufficient ionic conductivity. But itis also important for the cathode to be porous so that reactants andproducts can move through it easily and to maximize the amount ofcatalyst surface area that is available for reaction. In variousarrangements, the cathode ion-conducting polymer makes up somewhere inthe range between 30 and 70 wt %, between 20 and 80 wt %, or between 10and 90 wt %, of the material in the cathode layer, or any other suitablerange. The wt % of ion-conducting polymer in the cathode is selected toresult in the cathode layer porosity and ion-conductivity that gives thehighest current density for CO_(x) reduction. Examples of materials thatcan be used for the reduction catalyst particles include but are notlimited to transition metals such as V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb,Mo, Au, Ru, Rh, Pd, Ag, Cd, Hf, Ta, W, Re, Ir, Pt, and Hg, andcombinations thereof, and/or any other suitable materials. Othercatalyst materials can include alkali metals, alkaline earth metals,lanthanides, actinides, and post transition metals, such as Sn, Si, Ga,Pb, Al, Tl, Sb, Te, Bi, Sm, Tb, Ce, Nd and In or combinations thereof,and/or any other suitable catalyst materials. Catalysts can be in theform of nanoparticles that range in size from approximately 1 to 100 nmor particles that range in size from approximately 0.2 to 10 nm orparticles in the size range of approximately 1-1000 nm or any othersuitable range.

The conductive support particles in the cathode can be carbon particlesin various forms. Other possible conductive support particles includeboron-doped diamond or fluorine-doped tin oxide. In one arrangement, theconductive support particles are Vulcan carbon. The conductive supportparticles can be nanoparticles. The size range of the conductive supportparticles is between approximately 20 nm and 1000 nm or any othersuitable range. It is especially useful if the conductive supportparticles are compatible with the chemicals that are present in thecathode 220 when the CRR is operating, are reductively stable, and havea high hydrogen production overpotential so that they do not participatein any electrochemical reactions.

In general, such conductive support particles are larger than thereduction catalyst particles, and each conductive support particle cansupport many reduction catalyst particles. FIG. 3 is a schematic drawingthat shows a possible morphology for two different kinds of catalystssupported on a catalyst support particle 310, such as a carbon particle.Catalyst particles 330 of a first type and second catalyst particles 350of a second type are attached to the catalyst support particle 310. Invarious arrangements, there is only one type of catalyst particle orthere are more than two types of catalyst particles attached to thecatalyst support particle 310.

Again, with reference to FIG. 2, the anode 240 contains a blend ofoxidation catalyst and an anode ion-conducting polymer. There aretradeoffs in choosing the amount of ion-conducting polymer in the anode.It is important to include enough anode ion-conducting polymer toprovide sufficient ionic conductivity. But it is also important for theanode to be porous so that reactants and products can move through iteasily, and to maximize the amount of catalyst surface area that isavailable for reaction. In various arrangements, the ion-conductingpolymer in the anode makes up approximately 50 wt % of the layer orbetween approximately 5 and 20 wt %, 10 and 90 wt %, between 20 and 80wt %, between 25 and 70 wt %, or any suitable range. It is especiallyuseful if the anode 240 can tolerate high voltages, such as voltagesabove about 1.2 V vs. a reversible hydrogen electrode. It is especiallyuseful if the anode 240 is porous in order to maximize the amount ofcatalyst surface area available for reaction and to facilitate gas andliquid transport.

There are a variety of oxidation reactions that can occur at the anodedepending on the reactant that is fed to the anode and the anodecatalyst(s). Table 3 lists oxidation reactions that can occur at theanode and some exemplary catalysts that support those reactions. Theoxidation catalyst can be in the form of a structured mesh or can be inthe form of particles. If the oxidation catalyst is in the form ofparticles, the particles can be supported by electronically-conductivesupport particles. The conductive support particles can benanoparticles. It is especially useful if the conductive supportparticles are compatible with the chemicals that are present in theanode 240 when the CRR is operating and are oxidatively stable so thatthey do not participate in any electrochemical reactions. It isespecially useful if the conductive support particles are chosen withthe voltage and the reactants at the anode in mind. In somearrangements, the conductive support particles are titanium, which iswell-suited for high voltages. In other arrangements, the conductivesupport particles are carbon, which can be most useful at low voltages.In general, such conductive support particles are larger than theoxidation catalyst particles, and each conductive support particle cansupport many oxidation catalyst particles. An example of such anarrangement is shown in FIG. 3 and is discussed above. In onearrangement, the oxidation catalyst is iridium ruthenium oxide. Examplesof other materials that can be used for the oxidation catalyst include,but are not limited to, those shown in Table 3. It should be understoodthat many of these metal catalysts can be in the form of oxides,especially under reaction conditions.

TABLE 3 Feed Anode Oxidation Material Reaction Exemplary CatalystsHydrogen H₂ 7 2H⁺ + 2e⁻ Pt, Ni, Ru, other transition metals, and alloysand oxides thereof Methane CH₄ + H₂O 7 CH₃OH + Pd, Pd alloys and oxides2H⁺ + 2e⁻ thereof Methane CH₄ + 2H₂O 7 CO₂ + Pt, Au, Pd, and alloys and8H⁺ + 8e⁻ oxides thereof Ammonia 2NH₃ 7 N₂ + 6H⁺ + 6e⁻ Ru, Pt and oxidesthereof Water 2H₂O 7 O₂ + 4H⁺ + 4e⁻ Ir, IrRu, PtIr, Pt, Au, Ni, NiFe,Mn, Stainless steel and oxides thereof

The ion-exchange layer 260 can include three sublayers: a cathode bufferlayer 225, a polymer electrolyte membrane (PEM) 265, and an optionalanode buffer layer 245. Some layers in the ion-exchange layer can beporous, but it is useful if at least one layer is nonporous so thatreactants and products of the cathode cannot pass to the anode and viceversa.

The polymer electrolyte membrane 265 has high ionic conductivity(greater than about 1 mS/cm), and is mechanically stable. Mechanicalstability can be evidenced in a variety of ways such as through hightensile strength, modulus of elasticity, elongation to break, and tearresistance. Many commercially-available membranes can be used for thepolymer electrolyte membrane 265. Examples include, but are not limitedto, various Nafion® formulations, GORE-SELECT, FumaPEM® (PFSA)(FuMA-Tech GmbH), and Aquivion (PFSA) (Solvay).

It is important to note that when the polymer electrolyte membrane 265is a cation conductor and is conducting protons, it contains a highconcentration of protons during operation of the CRR, while the cathode220 operates best when a low concentration of protons is present. It canbe useful to include a cathode buffer layer 225 between the polymerelectrolyte membrane 265 and the cathode 220 to provide a region oftransition from a high concentration of protons to a low concentrationof protons. In one arrangement, the cathode buffer layer 225 is anion-conducting polymer with many of the same properties as theion-conducting polymer in the cathode 220. The cathode buffer layer 225provides a region for the proton concentration to transition from thepolymer electrolyte membrane 265, which has a high concentration ofprotons to the cathode 220, which has a low proton concentration. Withinthe cathode buffer layer 225, protons from the polymer electrolytemembrane 265 encounter anions from the cathode 220, and they neutralizeone another. The cathode buffer layer 225 helps ensure that adeleterious number of protons from the polymer electrolyte membrane 265does not reach the cathode 220 and raise the proton concentration. Ifthe proton concentration of the cathode 220 is too high, CO_(x)reduction does not occur. High proton concentration is considered to bein the range of approximately 10 to 0.1 molar and low concentration isconsidered to be less than approximately 0.01 molar.

The cathode buffer layer 225 can include a single polymer or multiplepolymers. If the cathode buffer layer 225 includes multiple polymers,the multiple polymers can be mixed together or can be arranged inseparate, adjacent layers. Examples of materials that can be used forthe cathode buffer layer 225 include, but are not limited to, FumaSepFAA-3, Sustainion®, Tokuyama anion exchange membrane material, andpolyether-based polymers, such as polyethylene oxide (PEO), and blendsthereof, and/or any other suitable ion-conducting polymer or material.The thickness of the cathode buffer layer is chosen to be sufficientthat CO_(x) reduction activity is high due to the proton concentrationbeing low. This sufficiency can be different for different cathodebuffer layer materials. In general, the thickness of the cathode bufferlayer is between approximately 200 nm and 100 between 300 nm and 75between 500 nm and 50 or any suitable range.

It can be useful if some or all of the following layers are porous: thecathode 220, the cathode buffer layer 225, the anode 240 and the anodebuffer layer 245. In some arrangements, porosity is achieved bycombining inert filler particles with the polymers in these layers.Materials that are suitable as inert filler particles include, but arenot limited to, TiO₂, silica, PTFE, zirconia, and alumina. In variousarrangements, the size of the inert filler particles is between 5 nm and500 between 10 nm and 100 μm, or any suitable size range. In otherarrangements, porosity is achieved by using particular processingmethods when the layers are formed. One example of such a processingmethod is laser ablation, where nano to micro-sized channels are formedin the layers. Laser ablation can additionally or alternatively achieveporosity in a layer by subsurface ablation. Subsurface ablation can formvoids within a layer, upon focusing the beam at a point within thelayer, and thereby vaporizing the layer material in the vicinity of thepoint. This process can be repeated to form voids throughout the layer,and thereby achieving porosity in the layer. The volume of a void ispreferably determined by the laser power (e.g., higher laser powercorresponds to a greater void volume), but can additionally oralternatively be determined by the focal size of the beam, or any othersuitable laser parameter. Another example is mechanically puncturing alayer to form channels through the layer. The porosity can have anysuitable distribution in the layer (e.g., uniform, an increasingporosity gradient through the layer, a random porosity gradient, adecreasing porosity gradient through the layer, a periodic porosity,etc.).

In some CRR reactions, bicarbonate is produced at the cathode 220. Itcan be useful if there is a polymer that blocks bicarbonate transportsomewhere between the cathode 220 and the anode 240, to preventmigration of bicarbonate away from the cathode. It can be thatbicarbonate takes some CO₂ with it as it migrates, which decreases theamount of CO₂ available for reaction at the cathode. In one arrangement,the polymer electrolyte membrane 265 includes a polymer that blocksbicarbonate transport. Examples of such polymers include, but are notlimited to, Nafion® formulations, GORE-SELECT, FumaPEM® (PFSA)(FuMA-Tech GmbH), and Aquivion (PFSA) (Solvay). In another arrangement,there is an anode buffer layer 245 between the polymer electrolytemembrane 265 and the anode 240, which blocks transport of bicarbonate.If the polymer electrolyte membrane is an anion-conductor, or does notblock bicarbonate transport, then an additional anode buffer layer toprevent bicarbonate transport can be useful. Materials that can be usedto block bicarbonate transport include, but are not limited to Nafion®formulations, GORE-SELECT, FumaPEM® (PFSA) (FuMA-Tech GmbH), andAquivion (PFSA) (Solvay). Of course, including a bicarbonate blockingfeature in the ion-exchange layer 260 is not particularly desirable ifthere is no bicarbonate in the CRR.

In another embodiment of the invention, the anode buffer layer 245provides a region for proton concentration to transition between thepolymer electrolyte membrane 265 to the anode 240. The concentration ofprotons in the polymer electrolyte membrane 265 depends both on itscomposition and the ion it is conducting. For example, a Nafion polymerelectrolyte membrane 265 conducting protons has a high protonconcentration. A FumaSep FAA-3 polymer electrolyte membrane 265conducting hydroxide has a low proton concentration. For example, if thedesired proton concentration at the anode 240 is more than 3 orders ofmagnitude different from the polymer electrolyte membrane 265, then ananode buffer layer 245 can be useful to effect the transition from theproton concentration of the polymer electrolyte membrane 265 to thedesired proton concentration of the anode. The anode buffer layer 245can include a single polymer or multiple polymers. If the anode bufferlayer 245 includes multiple polymers, the multiple polymers can be mixedtogether or can be arranged in separate, adjacent layers. Materials thatcan be useful in providing a region for the pH transition include, butare not limited to, Nafion, FumaSep FAA-3, Sustainion®, Tokuyama anionexchange polymer, and polyether-based polymers, such as polyethyleneoxide (PEO), blends thereof, and/or any other suitable materials. Highproton concentration is considered to be in the range of approximately10 to 0.1 molar and low concentration is considered to be less thanapproximately 0.01 molar. Ion-conducting polymers can be placed indifferent classes based on the type(s) of ions they conduct. This hasbeen discussed in more detail above. There are three classes ofion-conducting polymers described in Table 4 below. In one embodiment ofthe invention, at least one of the ion-conducting polymers in thecathode 220, anode 240, polymer electrolyte membrane 265, cathode bufferlayer 225, and anode buffer layer 245 is from a class that is differentfrom at least one of the others.

TABLE 4 Ion-Conducting Polymers Class Description Common FeaturesExamples A. Anion- Greater than Positively charged aminated tetramethylconducting approximately 1 mS/cm functional groups are polyphenylene;specific conductivity covalently bound to poly(ethylene-co- for anions,which have the polymer tetrafluoroethylene)-based a transference numberbackbone quaternary ammonium greater than polymer; quaternizedapproximately 0.85 at polysulfone around 100 micron thickness B.Conducts Greater than Salt is soluble in the polyethylene oxide; bothanions and approximately 1 mS/cm polymer and the salt polyethyleneglycol; cations conductivity for ions ions can move poly(vinylidenefluoride); (including both cations through the polymer polyurethane andanions), which have material a transference number between approximately0.15 and 0.85 at around 100 micron thickness C. Cation- Greater thanNegatively charged perfluorosulfonic acid conducting approximately 1mS/cm functional groups polytetrafluoroethylene specific conductivityare covalently bound to co-polymer; sulfonated for cations, which havethe polymer poly(ether ether ketone); a transference number backbonepoly(styrene sulfonic acid- greater than co-maleic acid) approximately0.85 at around 100 micron thickness

Some Class A ion-conducting polymers are known by tradenames such as2259-60 (Pall RAI), AHA by Tokuyama Co, Fumasep® FAA-3 (fumatech GbbH),Sustanion®, Morgane ADP by Solvay, or Tosflex® SF-17 by Tosoh anionexchange membrane material. Some Class C ion-conducting polymers areknown by tradenames such as various formulations of Nafion® (DuPont™),GORE-SELECT® (Gore), Fumapem® (fumatech GmbH), and Aquivion PFSA(Solvay).

A new membrane electrode assembly (MEA) 400 for use in a CRR is shown inFIG. 4, according to another embodiment of the invention. The MEA 400has a cathode 420, an anode 440, and an ion-conducting polymer layer460. The ion-conducting polymer layer 460 contains an ion-conductingpolymer membrane 465 and a cathode buffer layer 425. The anode 440 andthe ion-conducting polymer membrane 465 contain ion-conducting polymersthat are cation conductors, and the ion-conducting polymer membrane 465does not allow for appreciable amounts of bicarbonate to reach the anode440, so no anode buffer layer is used here.

A new membrane electrode assembly (MEA) 500 for use in a CRR is shown inFIG. 5, according to yet another embodiment of the invention. The MEA500 has a cathode 520, an anode 540, and an ion-conducting polymermembrane 560. In this arrangement, the transition from a high protonconcentration within the ion-conducting polymer membrane 560 to a lowproton concentration in the cathode layer is achieved at the interfaceof the cathode layer 520 and the ion-conducting polymer membrane 560, sono additional buffer layer between these two layers is used. The abilityto achieve the difference in proton concentration without the bufferlayer depends on the kinds of ion-conducting polymers used in thecathode layer 520 and in the ion-conducting polymer membrane 560 and theway in which the ion-conducting polymers mix at the interface of thelayers.

In another specific example, the membrane electrode assembly includes acathode layer including a reduction catalyst and a firstanion-conducting polymer (e.g., Sustainion, FumaSep FAA-3, Tokuyamaanion exchange polymer), an anode layer including an oxidation catalystand a first cation-conducting polymer (e.g., PFSA polymer), a membranelayer including a second cation-conducting polymer and arranged betweenthe cathode layer and the anode layer to conductively connect thecathode layer and the anode layer, and a cathode buffer layer includinga second anion-conducting polymer (e.g., Sustainion, FumaSep FAA-3,Tokuyama anion exchange polymer) and arranged between the cathode layerand the membrane layer to conductively connect the cathode layer and themembrane layer. In this example, the cathode buffer layer can have aporosity between about 1 and 90 percent by volume, but can additionallyor alternatively have any suitable porosity (including, e.g., noporosity). In other examples the cathode layer can have any suitableporosity (e.g., between 0.01-95%, 0.1-95%, 0.01-75%, 1-95%, 1-90%,etc.).

In a related example, the membrane electrode assembly can include ananode buffer layer that includes a third cation-conducting polymer, andis arranged between the membrane layer and the anode layer toconductively connect the membrane layer and the anode layer. The anodebuffer layer preferably has a porosity between about 1 and 90 percent byvolume, but can additionally or alternatively have any suitable porosity(including, e.g., no porosity). However, in other arrangements andexamples, the anode buffer layer can have any suitable porosity (e.g.,between 0.01-95%, 0.1-95%, 0.01-75%, 1-95%, 1-90%, etc.).

In another specific example, the membrane electrode assembly includes acathode layer including a reduction catalyst and a firstanion-conducting polymer (e.g., Sustainion, FumaSep FAA-3, Tokuyamaanion exchange polymer), an anode layer including an oxidation catalystand a first cation-conducting polymer, a membrane layer including asecond anion-conducting polymer (e.g., Sustainion, FumaSep FAA-3,Tokuyama anion exchange polymer) and arranged between the cathode layerand the anode layer to conductively connect the cathode layer and theanode layer, and an anode buffer layer including a secondcation-conducting polymer and arranged between the anode layer and themembrane layer to conductively connect the anode layer and the membranelayer.

In a related example, the membrane electrode assembly can include acathode buffer layer that includes a third anion-conducting polymer, andis arranged between the cathode layer and the membrane layer toconductively connect the cathode layer and the membrane layer. The thirdanion-conducting polymer can be the same or different from the firstand/or second anion-conducting polymer, The cathode buffer layerpreferably has a porosity between about 1 and 90 percent by volume, butcan additionally or alternatively have any suitable porosity (including,e.g., no porosity). However, in other arrangements and examples, thecathode buffer layer can have any suitable porosity (e.g., between0.01-95%, 0.1-95%, 0.01-75%, 1-95%, 1-90%, etc.).

The porosities (e.g., of the cathode buffer layer, of the anode bufferlayer, of the membrane layer, of the cathode layer, of the anode layer,of other suitable layers, etc.) of the examples described above andother examples and variations preferably have a uniform distribution,but can additionally or alternatively have any suitable distribution(e.g., a randomized distribution, an increasing gradient of pore sizethrough or across the layer, a decreasing gradient of pore size throughor across the layer, etc.). The porosity can be formed by any suitablemechanism, such as inert filler particles (e.g., diamond particles,boron-doped diamond particles, polyvinylidene difluoride/PVDF particles,polytetrafluoroethylene/PTFE particles, etc.) and any other suitablemechanism for forming substantially non-reactive regions within apolymer layer. The inert filler particles can have any suitable size,such as a minimum of about 10 nanometers and a maximum of about 200nanometers, and/or any other suitable dimension or distribution ofdimensions.

CO_(x) Reduction Reactor (CRR)

FIG. 6 is a schematic drawing that shows the major components of aCO_(x) reduction reactor (CRR) 605, according to an embodiment of theinvention.

The CRR 605 has a membrane electrode assembly 600 as described above inreference to FIG. 2. The membrane electrode assembly 600 has a cathode620 and an anode 640, separated by an ion-exchange layer 660. Theion-exchange layer 660 can include three sublayers: a cathode bufferlayer 625, a polymer electrolyte membrane 665, and an optional anodebuffer layer 645. In addition, the CRR 605 has a cathode supportstructure 622 adjacent to the cathode 620 and an anode support structure642 adjacent to the anode 640.

In one embodiment of the invention, the cathode 620 contains anion-conducting polymer as described in Class A in Table 4 above, theanode 640 contains an ion-conducting polymer as described in Class C inTable 4 above, and the polymer electrolyte membrane 665 contains anion-conducting polymer as described as Class C in Table 4 above. In onearrangement, the cathode buffer layer 625 contains at least twoion-conducting polymers: one as described in Class A and one asdescribed in Class B in Table 4 above.

In another embodiment of the invention, the cathode 620 contains both anion-conducting polymer as described in Class A and an ion-conductingpolymer as described in Class B, the anode 640 contains anion-conducting polymer as described in Class C, the polymer electrolytemembrane 665 contains an ion-conducting polymer as described in Class A,the cathode buffer layer 625 contains both an ion-conducting polymer asdescribed in Class A and an ion-conducting polymer as described in ClassB, and the anode buffer layer 645 contains an ion-conducting polymer asdescribed in Class C. Other combinations of ion-conducting polymers arealso possible.

The cathode support structure 622 has a cathode polar plate 624, usuallymade of graphite, to which a voltage can be applied. There can be flowfield channels, such as serpentine channels, cut into the insidesurfaces of the cathode polar plate 624. There is also a cathode gasdiffusion layer 626 adjacent to the inside surface of the cathode polarplate 624. In some arrangements, there is more than one cathode gasdiffusion layer (not shown). The cathode gas diffusion layer 626facilitates the flow of gas into and out of the membrane electrodeassembly 600. An example of a cathode gas diffusion layer 626 is acarbon paper that has a carbon microporous layer.

The anode support structure 642 has an anode polar plate 644, usuallymade of metal, to which a voltage can be applied. There can be flowfield channels, such as serpentine channels, cut into the insidesurfaces of the anode polar plate 644. There is also an anode gasdiffusion layer 646 adjacent to the inside surface of the anode polarplate 644. In some arrangements, there is more than one anode gasdiffusion layer (not shown). The anode gas diffusion layer 646facilitates the flow of gas into and out of the membrane electrodeassembly 600. An example of an anode gas diffusion layer 646 is atitanium mesh or titanium felt. In some arrangements, the gas diffusionlayers 626, 646 are microporous.

There are also inlets and outlets (not shown) associated with thesupport structures 622, 642, which allow flow of reactants and products,respectively, to the membrane electrode assembly 600. There are alsovarious gaskets (not shown) that prevent leakage of reactants andproducts from the cell.

In one embodiment of the invention, a direct current (DC) voltage isapplied to the membrane electrode assembly 600 through the cathode polarplate 624 and the anode polar plate 642. Water is supplied to the anode640 and is oxidized over an oxidation catalyst to form molecular oxygen(O2), releasing protons (H+) and electrons (e−). The protons migratethrough the ion-exchange layer 660 toward the cathode 620. The electronsflow through an external circuit (not shown). In one embodiment of theinvention, the reaction is described as follows: 2H₂O—4H⁺+4e⁻+O₂

In other embodiments of the invention, other reactants can be suppliedto the anode 640 and other reactions can occur. Some of these are listedin Table 3 above.

The flow of reactants, products, ions, and electrons through a CRR 705reactor is indicated in FIG. 7, according to an embodiment of theinvention.

The CRR 705 has a membrane electrode assembly 700 as described above inreference to FIG. 2. The membrane electrode assembly 700 has a cathode720 and an anode 740, separated by an ion-exchange layer 760. Theion-exchange layer 760 can include three sublayers: a cathode bufferlayer 725, a polymer electrolyte membrane 765, and an optional anodebuffer layer 745. In addition, the CRR 705 has a cathode supportstructure 722 adjacent to the cathode 720 and an anode support structure742 adjacent to the anode 740.

The cathode support structure 722 has a cathode polar plate 724, usuallymade of graphite, to which a voltage can be applied. There can be flowfield channels, such as serpentine channels, cut into the insidesurfaces of the cathode polar plate 724. There is also a cathode gasdiffusion layer 726 adjacent to the inside surface of the cathode polarplate 724. In some arrangements, there is more than one cathode gasdiffusion layer (not shown). The cathode gas diffusion layer 726facilitates the flow of gas into and out of the membrane electrodeassembly 700. An example of a cathode gas diffusion layer 726 is acarbon paper that has a carbon microporous layer.

The anode support structure 742 has an anode polar plate 744, usuallymade of metal, to which a voltage can be applied. There can be flowfield channels, such as serpentine channels, cut into the insidesurfaces of the anode polar plate 744. There is also an anode gasdiffusion layer 746 adjacent to the inside surface of the anode polarplate 744. In some arrangements, there is more than one anode gasdiffusion layer (not shown). The anode gas diffusion layer 746facilitates the flow of gas into and out of the membrane electrodeassembly 700. An example of an anode gas diffusion layer 746 is atitanium mesh or titanium felt. In some arrangements, the gas diffusionlayers 726, 746 are microporous.

There can also be inlets and outlets associated with the supportstructures 722, 742, which allow flow of reactants and products,respectively, to the membrane electrode assembly 700. There can also bevarious gaskets that prevent leakage of reactants and products from thecell.

CO_(x) can be supplied to the cathode 720 and reduced over CO_(x)reduction catalysts in the presence of protons and electrons. The CO_(x)can be supplied to the cathode 720 at pressures between 0 psig and 1000psig or any other suitable range. The CO_(x) can be supplied to thecathode 720 in concentrations below 100% or any other suitablepercentage along with a mixture of other gases. In some arrangements,the concentration of CO_(x) can be as low as approximately 0.5%, as lowas 5%, or as low as 20% or any other suitable percentage.

In one embodiment of the invention, between approximately 10% and 100%of unreacted CO_(x) is collected at an outlet adjacent to the cathode720, separated from reduction reaction products, and then recycled backto an inlet adjacent to the cathode 720. In one embodiment of theinvention, the oxidation products at the anode 740 are compressed topressures between 0 psig and 1500 psig.

In one embodiment of the invention, multiple CRRs (such as the one shownin FIG. 6) are arranged in an electrochemical stack and are operatedtogether. The CRRs that make up the individual electrochemical cells ofthe stack can be connected electrically in series or in parallel.Reactants are supplied to individual CRRs and reaction products are thencollected.

The major inputs and outputs to the reactor are shown in FIG. 8. CO_(x),anode feed material, and electricity are fed to the reactor. CO_(x)reduction product and any unreacted CO_(x) leave the reactor. UnreactedCO_(x) can be separated from the reduction product and recycled back tothe input side of the reactor. Anode oxidation product and any unreactedanode feed material leave the reactor in a separate stream. Unreactedanode feed material can be recycled back to the input side of thereactor.

Various catalysts in the cathode of a CRR cause different products ormixtures of products to form from CO_(x) reduction reactions. Examplesof possible CO_(x) reduction reactions at the cathode are described asfollows:

CO₂+2H⁺+2e ⁻7CO+H₂O

2CO₂+12H⁺+12e ⁻7CH₂CH₂+4H₂O

2CO₂+12H⁺+12e ⁻7CH₃CH₂OH+3H₂O

CO₂+8H⁺+8e ⁻7CH₄+2H₂O

2CO+8H⁺+8e ⁻7CH₂CH₂+2H₂O

2CO+8H⁺+8e ⁻7CH₃CH₂OH+H₂O

CO+6H⁺+8e ⁻7CH₄+H₂O

In another embodiment of the invention, a method of operating a CO_(x)reduction reactor, as described in the embodiments of the inventionabove, is provided. It involves applying a DC voltage to the cathodepolar plate and the anode polar plate, supplying oxidation reactants tothe anode and allowing oxidation reactions to occur, supplying reductionreactants to the cathode and allowing reduction reactions to occur,collecting oxidation reaction products from the anode; and collectingreduction reaction products from the cathode.

In one arrangement, the DC voltage is greater than −1.2V. In variousarrangements, the oxidation reactants can be any of hydrogen, methane,ammonia, water, or combinations thereof, and/or any other suitableoxidation reactants. In one arrangement, the oxidation reactant iswater. In various arrangements, the reduction reactants can be any ofcarbon dioxide, carbon monoxide, and combinations thereof, and/or anyother suitable reduction reactants. In one arrangement, the reductionreactant is carbon dioxide.

In another specific example, the CO_(x) reduction reactor includes amembrane electrode assembly, which includes a cathode layer thatincludes a reduction catalyst and a first anion-conducting polymer(e.g., FumaSep FAA-3, Sustainion, Tokuyama anion exchange polymer). Thereactor also includes an anode layer that includes an oxidation catalystand a first cation-conducting polymer (e.g., Nafion 324, Nafion 350,Nafion 417, Nafion 424, Nafion 438, Nafion 450, Nafion 521, Nafion 551,other Nafion formulations, Aquivion, GORE-SELECT, Flemion, PSFA, etc.).The reactor also includes a membrane layer that includes a secondcation-conducting polymer, wherein the membrane layer is arrangedbetween the cathode layer and the anode layer and conductively connectsthe cathode layer and the anode layer. The reactor also includes acathode manifold coupled to the cathode layer, and an anode manifoldcoupled to the anode layer. In this example, the cathode manifold caninclude a cathode support structure adjacent to the cathode layer,wherein the cathode support structure includes a cathode polar plate, acathode gas diffusion layer arranged between the cathode polar plate andthe cathode layer, a first inlet fluidly connected to the cathode gasdiffusion layer, and a first outlet fluidly connected to the cathode gasdiffusion layer. Also in this example, the anode manifold can include ananode support structure adjacent to the anode layer, wherein the anodesupport structure includes an anode polar plate, an anode gas diffusionlayer arranged between the anode polar plate and the anode layer, asecond inlet fluidly connected to the anode gas diffusion layer, and asecond outlet fluidly connected to the anode gas diffusion layer. In arelated example, the membrane electrode assembly of the reactor includesa cathode buffer layer that includes a second anion-conducting polymer(e.g., FumaSep FAA-3, Sustainion, Tokuyama anion exchange polymer), andis arranged between the cathode layer and the membrane layer andconductively connects the cathode layer and the membrane layer. Thebuffer layer(s) of this example (e.g., cathode buffer layer, anodecathode layer) can have a porosity between about 1 and 90 percent byvolume, but can alternatively have any suitable porosity (including,e.g., no porosity). However, in other arrangements and examples, thebuffer layer(s) can have any suitable porosity (e.g., between 0.01-95%,0.1-95%, 0.01-75%, 1-95%, 1-90%, etc.). In a related example, the firstand second anion-conducting polymers of the membrane electrode assemblycan be the same anion-conducting polymer (e.g., comprised of identicalpolymer formulations).

This invention has been described herein in considerable detail toprovide those skilled in the art with information relevant to apply thenovel principles and to construct and use such specialized components asare required. However, it is to be understood that the invention can becarried out by different equipment, materials and devices, and thatvarious modifications, both as to the equipment and operatingprocedures, can be accomplished without departing from the scope of theinvention itself.

1.-22. (canceled)
 23. A membrane electrode assembly comprising: acathode layer comprising a reduction catalyst; an anode layer comprisingan oxidation catalyst; a membrane layer comprising a firstcation-conducting polymer, the membrane layer arranged between thecathode layer and the anode layer, the membrane layer conductivelyconnecting the cathode layer and the anode layer; and a cathode bufferlayer comprising a first anion-conducting polymer, wherein the cathodebuffer layer is arranged between the cathode layer and the membranelayer and conductively connects the cathode layer and the membranelayer, wherein the cathode buffer layer is porous such that gas can betransported in the cathode buffer layer and wherein the membrane layeris non-porous such that gas is prevented from passing between thecathode layer and the anode layer.
 24. The membrane electrode assemblyof claim 23, further comprising an anode buffer layer, comprising asecond cation-conducting polymer, arranged between the membrane layerand the anode layer.
 25. The membrane electrode assembly of claim 24,wherein the first and second cation-conducting polymers comprise aperfluorosulfonic acid (PFSA) polymer, and wherein the anode bufferlayer is porous.
 26. The membrane electrode assembly of claim 23,wherein the cathode buffer layer further comprises inert fillerparticles that form a porosity of the cathode buffer layer.
 27. Themembrane electrode assembly of claim 26, wherein the inert fillerparticles comprise at least one of diamond particles, boron-dopeddiamond particles, polyvinylidene difluoride (PVDF) particles, andpolytetrafluoroethylene (PTFE) particles.
 28. The membrane electrodeassembly of claim 27, wherein a size of each of the inert fillerparticles is between about 10 nanometers and about 200 nanometers. 29.The membrane electrode assembly of claim 23, wherein the firstanion-conducting polymer is selected from a group consisting ofSustainion, FumaSep FAA-3, and Tokuyama anion exchange polymer.
 30. Themembrane electrode assembly of claim 23, wherein the cathode layerfurther comprises a second anion-conducting polymer.
 31. The membraneelectrode assembly of claim 30, wherein the first anion-conductingpolymer and the second anion-conducting polymer are the same polymer.32. The membrane electrode assembly of claim 30, wherein the firstanion-conducting polymer and the second anion-conducting polymer areSustainion.
 33. The membrane electrode assembly of claim 23, wherein theanode layer further comprises a second cation-conducting polymer. 34.The membrane electrode assembly of claim 33, wherein the firstcation-conducting polymer and the second cation-conducting polymer arethe same polymer.
 35. The membrane electrode assembly of claim 23,wherein the thickness of the cathode buffer layer is between 200 nm and100 μm.
 36. The membrane electrode assembly of claim 23, wherein thecathode buffer layer has a porosity between 0.1% and 95%.
 37. A COxreduction reactor comprising: a membrane electrode assembly comprising:a cathode layer comprising a reduction catalyst; an anode layercomprising an oxidation catalyst; a membrane layer comprising a firstcation-conducting polymer, the membrane layer arranged between thecathode layer and the anode layer, the membrane layer conductivelyconnecting the cathode layer and the anode layer; and a cathode bufferlayer comprising a first anion-conducting polymer, wherein the cathodebuffer layer is arranged between the cathode layer and the membranelayer and conductively connects the cathode layer and the membranelayer, wherein the cathode buffer layer is porous such that gas can betransported in the cathode buffer layer and wherein the membrane layeris non-porous such that gas is prevented from passing between thecathode layer and the anode layer; a cathode manifold coupled to thecathode layer; and an anode manifold coupled to the anode layer.
 38. TheCO_(x) reduction reactor of claim 37, wherein the cathode manifoldcomprises a cathode support structure adjacent to the cathode layer, thecathode support structure comprising: a cathode polar plate; a cathodegas diffusion layer arranged between the cathode polar plate and thecathode layer; a first inlet fluidly connected to the cathode gasdiffusion layer; and a first outlet fluidly connected to the cathode gasdiffusion layer; and wherein the anode manifold comprises an anodesupport structure adjacent to the anode layer, the anode supportstructure comprising: an anode polar plate; an anode gas diffusion layerarranged between the anode polar plate and the anode layer; a secondinlet fluidly connected to the anode gas diffusion layer; and a secondoutlet fluidly connected to the anode gas diffusion layer.
 39. TheCO_(x) reduction reactor of claim 37, wherein the cathode layer furthercomprises a second anion-conducting polymer.
 40. The CO_(x) reductionreactor of claim 37, wherein the anode layer further comprises a secondcation-conducting polymer.
 41. The CO_(x) reduction reactor of claim 37,wherein the thickness of the cathode buffer layer is between 200 nm and100 μm.
 42. The CO_(x) reduction reactor of claim 37, wherein thecathode buffer layer has a porosity between 0.1% and 95%.